Benign spinal meningioma without dural attachment presenting delayed CSF dissemination and malignant transformation

Benign spinal meningiomas have good prognoses, with low rates of recurrence and no cerebrospinal fluid (CSF) dissemination. However, we experienced an extremely rare case of initially benign non-dura-based spinal meningioma that showed multiple CSF disseminated lesions, which progressed for 14 years. A 29-year-old woman without neurofibromatosis presented with progressing dysesthesia in her lower limbs, low back pain, and intermittent claudication. Magnetic resonance imaging (MRI) showed an intradural extramedullary mass lesion at the Th10/11 level. The patient underwent a tumor resection. Intraoperative findings indicated that the tumor had no dural attachment. Histopathological diagnosis after gross total removal was microcystic meningioma (grade I, WHO 2007). Seven years after the first operation, other lesions appeared at the levels of Th11/12, L1, and L2/3 in MRI. These tumors were slow growing and became symptomatic; thus, a second surgery was performed 14 years after the first operation. The histopathological diagnosis was atypical meningioma (grade II, WHO 2007). Benign spinal meningiomas show CSF dissemination extremely rarely, although some authors have reported non-dura-based intraspinal clear-cell meningiomas showing CSF dissemination. However, even in cases of WHO grade I, neurosurgeons should pay attention to late CSF dissemination and malignant transformation after surgical removal of non-dura-based intraspinal meningiomas.